go PRACTICAL HISTOLOGY. 



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7EESIT 



V 



THE SKIN. 



THE skin consists of (a] the epidermis, (b} the corium (cutis vera or true skin, with the papillae), 

 whilst deeper down is (V) subcutaneous tissue containing fat-cells. 



The epidermis is made up of several layers ; the most superficial is ( I ) the stratum corneum, 

 or horny layer, composed of layers of flattened epithelium about to be thrown off. It varies 

 in thickness, being thickest where there is most pressure, e.g. palms of the hands and soles of 

 the feet. Below this is (2) the stratum lucidum, a narrow, clear, homogeneous, easily-recognised 

 layer. In it the epithelial cells are closely packed together, and each one contains a flattened 

 nucleus. Then follows (3) the stratum granule sum (Unna), or the ' stratum of granular cells ' 

 (of Langerhans). It is best seen where the skin is thick, and consists of two or more layers 

 of spindle-shaped ' granular ' and nucleated cells, which become deeply stained with the 

 carmine of picrocarmine, and also with logwood, so that it forms a marked feature in a stained 

 section. The ' granular ' appearance is due to the presence of granules of some albuminoid 

 matter, probably closely related to keratin. The deepest layer (4), rete mucosum, or rete 

 Malpighii, or stratum Malpighii, consists of several layers of epithelium ; the deepest layers 

 are composed of small columnar cells, with oval nuclei, whilst those of the middle layers are 

 more or less polyhedral, with spherical nuclei. In this layer is deposited the pigment in 

 coloured individuals. In it ' prickle ' cells are easily seen. This layer rests on the true skin, 

 and also dips down between the papillae of the true skin. 



The corium has, projecting from its superficial surface, a series of conical or cylindrical 

 papilla, which vary in size and number in different localities, being most numerous where the 

 sense of touch is most acute, e.g. palms of the hands and soles of the feet. The papillae and the 

 remainder of the true skin consist of bundles of fibrous tissue, which interlace in a very complex 

 manner, so as to form a dense tissue, and in it are to be seen connective-tissue corpuscles 

 and interfascicular lymph-spaces, and in it lie gland-ducts, blood-vessels, nerves, hairs, &c. 

 It also contains many elastic fibres, which are most numerous in the subcutaneous tissue and 

 fewest in the papillae. They are arranged with reference to the surface of the trabeculae of 

 fibrous tissue. 



The subcutaneous tissue contains groups of fat-cells, and between them septa of fibrous 

 tissue. 



The skin also contains sweat-glands, and in certain places sebaceous glands and hair- 

 follicles, and numerous nerves and their terminations, blood-vessels, and lymphatics. 



PREPARATION (a) Chromic acid and Spirit Mixture. Place small pieces of the skin from 

 various parts, e.g. from the palm of the hand, fingers, or sole of the foot, and scalp, in the 

 above fluid for ten days, and complete the hardening in spirit. Make vertical sections with a 

 freezing microtome, and stain some with logwood, and mount them in dammar ; others should 

 be stained with picrocarmine, and mounted in Farrant's solution, whilst others again are to be 



